Date:	Thu, 8 Feb 2007 18:01:49 +0900
From:	"Takashi Sato" <sho@...s.nec.co.jp>
To:	linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: [RFC][PATCH 2/3] Move the file data to the new blocks

Move the blocks on the temporary inode to the original inode
by a page.
1. Read the file data from the old blocks to the page
2. Move the block on the temporary inode to the original inode
3. Write the file data on the page into the new blocks

Signed-off-by: Takashi Sato <sho@...s.nec.co.jp>
---
diff -Nrup -X linux-2.6.19-rc6.org/Documentation/dontdiff linux-2.6.19-rc6-1/fs/ext4/extents.c linux-2.6.19-rc6-full/fs/ext4/extents.c
--- linux-2.6.19-rc6-1/fs/ext4/extents.c	2007-02-08 14:13:49.000000000 +0900
+++ linux-2.6.19-rc6-full/fs/ext4/extents.c	2007-02-08 14:09:43.000000000 +0900
@@ -2533,6 +2533,653 @@ ext4_ext_next_extent(struct inode *inode
 }
 
 /**
+ * ext4_ext_merge_across - merge extents across leaf block
+ * 
+ * @handle	journal handle
+ * @inode	target file's inode
+ * @o_start	first original extent to be defraged
+ * @o_end	last original extent to be defraged
+ * @start_ext	first new extent to be merged
+ * @new_ext	middle of new extent to be merged
+ * @end_ext	last new extent to be merged
+ *
+ * This function returns 0 if succeed, otherwise returns error value.
+ */
+static int
+ext4_ext_merge_across_blocks(handle_t *handle, struct inode *inode,
+		struct ext4_extent *o_start,
+		struct ext4_extent *o_end, struct ext4_extent *start_ext,
+		struct ext4_extent *new_ext,struct ext4_extent *end_ext)
+{
+	struct ext4_ext_path *org_path = NULL;
+	unsigned long eblock = 0;
+	int err = 0;
+	int new_flag = 0;
+	int end_flag = 0;
+
+	if (le16_to_cpu(start_ext->ee_len) &&
+		le16_to_cpu(new_ext->ee_len) &&
+		le16_to_cpu(end_ext->ee_len)) {
+
+		if ((o_start) == (o_end)) {
+
+			/*       start_ext   new_ext    end_ext
+			 * dest |---------|-----------|--------|
+			 * org  |------------------------------|
+			 */
+
+			ext4_free_blocks(handle, inode, ext_pblock(o_start) +
+                                le16_to_cpu(start_ext->ee_len),
+                                le16_to_cpu(new_ext->ee_len), 0);
+
+			end_flag = 1;
+
+		} else {
+
+			/*       start_ext   new_ext   end_ext
+			 * dest |---------|----------|---------|
+			 * org  |---------------|--------------|
+			 */
+
+			ext4_free_blocks(handle, inode, ext_pblock(o_start) +
+				le16_to_cpu(start_ext->ee_len),
+				le16_to_cpu(o_start->ee_len)
+				- le16_to_cpu(start_ext->ee_len), 0);
+
+			ext4_free_blocks(handle, inode, ext_pblock(o_end),
+				le16_to_cpu(o_end->ee_len)
+				- le16_to_cpu(end_ext->ee_len), 0);
+
+			o_end->ee_block = end_ext->ee_block;
+			o_end->ee_len = end_ext->ee_len;
+			ext4_ext_store_pblock(o_end, ext_pblock(end_ext));
+		}
+
+		o_start->ee_len = start_ext->ee_len;
+		new_flag = 1;
+
+	} else if ((le16_to_cpu(start_ext->ee_len)) &&
+			(le16_to_cpu(new_ext->ee_len)) &&
+			(!le16_to_cpu(end_ext->ee_len)) &&
+			((o_start) == (o_end))) {
+
+		/*         start_ext        new_ext
+		 * dest |--------------|---------------|
+		 * org  |------------------------------|
+		 */
+
+		ext4_free_blocks(handle, inode, ext_pblock(o_start) +
+			le16_to_cpu(start_ext->ee_len),
+			le16_to_cpu(new_ext->ee_len), 0);
+
+		o_start->ee_len = start_ext->ee_len;
+		new_flag = 1;
+
+	} else if ((!le16_to_cpu(start_ext->ee_len)) &&
+			(le16_to_cpu(new_ext->ee_len)) &&
+			(le16_to_cpu(end_ext->ee_len)) &&
+			((o_start) == (o_end))) {
+
+		/*          new_ext        end_ext
+		 * dest |--------------|---------------|
+		 * org  |------------------------------|
+		 */
+
+		ext4_free_blocks(handle, inode, ext_pblock(o_end),
+			le16_to_cpu(new_ext->ee_len), 0);
+
+		o_end->ee_block = end_ext->ee_block;
+		o_end->ee_len = end_ext->ee_len;
+		ext4_ext_store_pblock(o_end, ext_pblock(end_ext));
+
+		/* If new_ext was first block */	
+		if (!new_ext->ee_block)
+			eblock = 0;
+		else
+			eblock = le32_to_cpu(new_ext->ee_block);
+
+		new_flag = 1;
+	} else {
+		printk("Unexpected case \n");
+		return -EIO;
+	}
+
+	if (new_flag) {
+		org_path = ext4_ext_find_extent(inode, eblock, NULL);
+		if (IS_ERR(org_path)) {
+			err = PTR_ERR(org_path);
+			org_path = NULL;
+			goto ERR;
+		}
+		err = ext4_ext_insert_extent(handle, inode,
+					org_path, new_ext);
+		if (err)
+			goto ERR;
+	}
+
+	if (end_flag) {
+		org_path = ext4_ext_find_extent(inode,
+					end_ext->ee_block -1, org_path);
+		if (IS_ERR(org_path)) {
+			err = PTR_ERR(org_path);
+			org_path = NULL;
+			goto ERR;
+		}
+		err = ext4_ext_insert_extent(handle, inode,
+					org_path, end_ext);
+		if (err)
+			goto ERR;
+	}
+ERR:
+	if (org_path) {
+		ext4_ext_drop_refs(org_path);
+		kfree(org_path);
+	}
+
+	return err;
+
+}
+
+/**
+ * ext4_ext_merge_inside_block - merge new extent to the extent block
+ *
+ * @handle	journal handle
+ * @inode	target file's inode
+ * @o_start	first original extent to be defraged
+ * @o_end	last original extent to be merged
+ * @start_ext	first new extent to be merged
+ * @new_ext	middle of new extent to be merged
+ * @end_ext	last new extent to be merged
+ * @eh		extent header of target leaf block
+ * @replaced	the number of blocks which will be replaced with new_ext
+ * @range_to_move used to dicide how to merge
+ *
+ * This function always returns 0.
+*/
+static int
+ext4_ext_merge_inside_block(handle_t *handle, struct inode *inode,
+		struct ext4_extent *o_start, struct ext4_extent *o_end,
+		struct ext4_extent *start_ext, struct ext4_extent *new_ext,
+		struct ext4_extent *end_ext, struct ext4_extent_header *eh,
+		ext4_fsblk_t replaced, int range_to_move)
+{
+	struct ext4_extent *free_start, *free_end;
+	int i = 0;
+	unsigned len;
+
+	/* Free old blocks
+	 * dest        |---------------|
+	 * org  |---------------|
+	 */
+	free_start = o_start;
+	free_end = o_end;
+	if (le16_to_cpu(start_ext->ee_len)) {
+		if (le16_to_cpu(o_start->ee_len)
+			> le16_to_cpu(start_ext->ee_len)) {
+			ext4_free_blocks(handle, inode,
+				ext_pblock(o_start)
+					+ le16_to_cpu(start_ext->ee_len),
+				le16_to_cpu(o_start->ee_len)
+					- le16_to_cpu(start_ext->ee_len), 0);
+		}
+		free_start++;
+	}
+
+	/* dest |----------------|
+	 * org          |---------------|
+	 */
+	if (le16_to_cpu(end_ext->ee_len)) {
+		ext4_free_blocks(handle, inode, ext_pblock(o_end),
+			le16_to_cpu(o_end->ee_len)
+				- le16_to_cpu(end_ext->ee_len), 0);
+		free_end--;
+	}
+
+	/* dest |-------------------|
+	 * org   |-----------------|
+	 */
+	for (; free_start <= free_end; free_start++) {
+		ext4_free_blocks(handle, inode,
+			ext_pblock(free_start),
+			le32_to_cpu(free_start->ee_len), 0);
+	}
+
+	/* Move the existing extents */
+	if (range_to_move && o_end < EXT_LAST_EXTENT(eh)) {
+		len = EXT_LAST_EXTENT(eh) - (o_end + 1) + 1;
+		len = len * sizeof(struct ext4_extent);
+		memmove(o_end + 1 + range_to_move, o_end + 1, len);
+	}
+
+	/* Insert start entry */
+	if (le16_to_cpu(start_ext->ee_len)) {
+		o_start[i++].ee_len = start_ext->ee_len;
+	}
+
+	/* Insert new entry */
+	if (le16_to_cpu(new_ext->ee_len)) {
+		o_start[i].ee_block = new_ext->ee_block;
+		o_start[i].ee_len = cpu_to_le16(replaced);
+		ext4_ext_store_pblock(&o_start[i++], ext_pblock(new_ext));
+	}
+
+	/* Insert end entry */
+	if (end_ext->ee_len) {
+		o_start[i] = *end_ext;
+	}
+
+	/* Increment the total entries counter on the extent block */
+	eh->eh_entries
+		= cpu_to_le16(le16_to_cpu(eh->eh_entries) + range_to_move);
+
+	return 0;
+}
+
+/**
+ * ext4_ext_merge_extents - merge new extent
+ *
+ * @handle      journal handle
+ * @inode       target file's inode
+ * @org_path    path indicates first extent to be defraged
+ * @o_start     first original extent to be defraged
+ * @o_end       last original extent to be defraged
+ * @start_ext   first new extent to be merged
+ * @new_ext     middle of new extent to be merged
+ * @end_ext     last new extent to be merged
+ * @replaced    the number of blocks which will be replaced with new_ext
+ *
+ * This function returns 0 if succeed, otherwise returns error value.
+ */
+static int
+ext4_ext_merge_extents(handle_t *handle, struct inode *inode,
+		struct ext4_ext_path *org_path,
+		struct ext4_extent *o_start, struct ext4_extent *o_end,
+		struct ext4_extent *start_ext, struct ext4_extent *new_ext,
+		struct ext4_extent *end_ext, ext4_fsblk_t replaced)
+{
+	struct  ext4_extent_header * eh;
+	unsigned need_slots, slots_range;
+	int	range_to_move, depth, ret;
+
+	/* The extents need to be inserted
+	 * start_extent + new_extent + end_extent
+	 */
+	need_slots = (le16_to_cpu(start_ext->ee_len) ? 1 : 0) +
+			(le16_to_cpu(end_ext->ee_len) ? 1 : 0) +
+			(le16_to_cpu(new_ext->ee_len) ? 1 : 0);
+
+	/* The number of slots between start and end */
+	slots_range = o_end - o_start + 1;
+
+	/* Range to move the end of extent */
+	range_to_move = need_slots - slots_range;
+	depth = org_path->p_depth;
+	org_path += depth;
+	eh = org_path->p_hdr;
+
+	if (depth) {
+		/* Register to journal */
+		if (ext4_journal_get_write_access(handle, org_path->p_bh))
+			return -EIO;
+	}
+
+	/* expansion */
+	if ((range_to_move > 0) && 
+		(range_to_move > le16_to_cpu(eh->eh_max)
+			- le16_to_cpu(eh->eh_entries))) {
+
+		if ((ret = ext4_ext_merge_across_blocks(handle, inode,
+				o_start, o_end, start_ext,
+				new_ext, end_ext)) < 0)
+			return ret;
+	} else {
+		if ((ret = ext4_ext_merge_inside_block(handle, inode,
+			o_start, o_end, start_ext, new_ext,
+			end_ext, eh, replaced, range_to_move)) < 0)
+			return ret;
+	}
+
+	if (depth) {
+		if (ext4_journal_dirty_metadata(handle, org_path->p_bh))
+			return -EIO;
+	} else {
+		if (ext4_mark_inode_dirty(handle, inode) < 0)
+			return -EIO;
+	}
+
+	return 0;
+
+}
+
+/**
+ * ext4_ext_defrag_leaf_block -  Defragmentation for one leaf extent block.
+ * @handle      journal handle
+ * @org_inode   target inode
+ * @org_path    path indicates first extent to be defraged
+ * @dext        destination extent
+ * @from        start offset on the target file
+ *
+ * This function returns 0 if succeed, otherwise returns error value.
+ */
+static int
+ext4_ext_defrag_leaf_block(handle_t *handle, struct inode *org_inode,
+		struct ext4_ext_path *org_path, struct ext4_extent *dext,
+		ext4_fsblk_t *from, ext4_fsblk_t *delete_start)
+{
+	unsigned long depth;
+	ext4_fsblk_t replaced = 0;
+	struct ext4_extent *oext, *o_start = NULL, *o_end = NULL, *prev_ext;
+	struct ext4_extent new_ext, start_ext, end_ext;
+	ext4_fsblk_t new_end;
+	ext4_fsblk_t lblock;
+	ext4_fsblk_t len;
+	ext4_fsblk_t new_phys_end;
+	int	ret;
+
+	depth = ext_depth(org_inode);
+	start_ext.ee_len = end_ext.ee_len = 0;
+	o_start = o_end = oext = org_path[depth].p_ext;
+	ext4_ext_store_pblock(&new_ext, ext_pblock(dext));	
+	len = new_ext.ee_len = dext->ee_len;
+	new_ext.ee_block = cpu_to_le32(*from);
+	lblock = le32_to_cpu(oext->ee_block);
+	new_end = le32_to_cpu(new_ext.ee_block)
+		+ le16_to_cpu(new_ext.ee_len) - 1;
+	new_phys_end = ext_pblock(&new_ext)
+		+ le16_to_cpu(new_ext.ee_len) - 1;
+
+	/* First original extent
+	 * dest         |---------------|
+	 * org  |---------------|
+	 */
+	if (le32_to_cpu(new_ext.ee_block) >
+		le32_to_cpu(oext->ee_block) &&
+		le32_to_cpu(new_ext.ee_block) <
+		le32_to_cpu(oext->ee_block)
+		+ le16_to_cpu(oext->ee_len)) {
+		start_ext.ee_len = cpu_to_le32(le32_to_cpu(new_ext.ee_block)
+					- le32_to_cpu(oext->ee_block));
+		replaced += le16_to_cpu(oext->ee_len)
+					- le16_to_cpu(start_ext.ee_len);
+	} else if (oext > EXT_FIRST_EXTENT(org_path[depth].p_hdr)) {
+		/* We can merge previous extent. */
+		prev_ext = oext -1;
+		if ((ext_pblock(prev_ext)
+			+ le32_to_cpu(prev_ext->ee_len))
+			== ext_pblock(&new_ext)) {
+			o_start = prev_ext;
+			start_ext.ee_len = cpu_to_le32(
+					le16_to_cpu(prev_ext->ee_len)
+					+ le16_to_cpu(new_ext.ee_len));
+			new_ext.ee_len = 0;
+		}
+	}
+	for (;;) {
+		/* The extent for destination must be found. */
+		BUG_ON(!oext || lblock != le32_to_cpu(oext->ee_block));
+		lblock += le16_to_cpu(oext->ee_len);
+
+		/* Middle of original extent
+		 * dest |-------------------|
+		 * org   |-----------------|
+		 */
+		if (le32_to_cpu(new_ext.ee_block) <=
+			le32_to_cpu(oext->ee_block) &&
+			new_end >= le32_to_cpu(oext->ee_block)
+			+ le16_to_cpu(oext->ee_len) -1) {
+			replaced += le16_to_cpu(oext->ee_len);
+		}
+
+		/* Last original extent
+		 * dest |----------------|
+		 * org          |---------------|
+		 */
+		if (new_end >= le32_to_cpu(oext->ee_block) &&
+			new_end < le32_to_cpu(oext->ee_block)
+				+ le16_to_cpu(oext->ee_len) - 1) {
+			end_ext.ee_len
+				= cpu_to_le16(le32_to_cpu(oext->ee_block)
+				+ le16_to_cpu(oext->ee_len) -1 - new_end);
+			ext4_ext_store_pblock(&end_ext, (ext_pblock(o_end)
+				+ cpu_to_le16(oext->ee_len)
+				- cpu_to_le16(end_ext.ee_len)));
+			end_ext.ee_block
+				= cpu_to_le32(le32_to_cpu(o_end->ee_block)
+				+ le16_to_cpu(oext->ee_len)
+				- le16_to_cpu(end_ext.ee_len));
+			replaced += le16_to_cpu(oext->ee_len)
+				- le16_to_cpu(end_ext.ee_len);
+		}
+
+		/* Detected the block end, reached the number of replaced
+		 * blocks to dext->ee_len.  Then, merge the extent.
+		 */
+		if (oext == EXT_LAST_EXTENT(org_path[depth].p_hdr) ||
+			new_end <= le32_to_cpu(oext->ee_block)
+				+ le16_to_cpu(oext->ee_len) - 1) {
+			if ((ret = ext4_ext_merge_extents(handle, org_inode,
+				org_path, o_start, o_end, &start_ext,
+				&new_ext, &end_ext, replaced)) < 0) {
+				return ret;
+			}
+
+			*delete_start = le32_to_cpu(new_ext.ee_block)
+							+ replaced;
+
+			/* All expected blocks are replaced */
+			if (new_ext.ee_len <= 0) {
+				if (DQUOT_ALLOC_BLOCK
+					(org_inode, len)) {
+					return -EDQUOT;
+				}
+				return 0;
+			}
+
+			/* re-calculate new_ext */
+			new_ext.ee_len = cpu_to_le32(le16_to_cpu(new_ext.ee_len)
+				- replaced);
+			new_ext.ee_block =
+				cpu_to_le32(le32_to_cpu(new_ext.ee_block)
+				+ replaced);
+			ext4_ext_store_pblock(&new_ext, ext_pblock(&new_ext)
+					 + replaced);
+			replaced = 0;
+			start_ext.ee_len = end_ext.ee_len = 0;
+			o_start = NULL;
+
+			/* All expected blocks are replaced */
+			if (new_ext.ee_len <= 0) {
+				if (DQUOT_ALLOC_BLOCK
+					(org_inode, len)) {
+					return -EDQUOT;
+				}
+				return 0;
+			}
+		}
+
+		/* Get next extent for original. */
+		if ((ret
+		 = ext4_ext_next_extent(org_inode, org_path, &oext))
+								!= 0) {
+			if (ret == 1)
+				ret = -EIO;
+			return ret;
+		}
+		o_end = oext;
+		if (!o_start)
+			o_start = oext;
+	}
+}
+
+/**
+ * ext4_ext_replace_branches - replace original extents with new extents.
+ * @org_inode    Original inode
+ * @dest_inode   temporary inode
+ * @from_page    Page offset
+ * @count_page   Page count to be replaced
+ * @delete_start block offset for deletion
+ *
+ * This function returns 0 if succeed, otherwise returns error value.
+ * Replace extents for blocks from "from" to "from+count-1".
+ */
+static int
+ext4_ext_replace_branches(struct inode *org_inode, struct inode *dest_inode,
+			pgoff_t from_page,  pgoff_t dest_from_page,
+			pgoff_t count_page, ext4_fsblk_t *delete_start) 
+{
+	struct ext4_ext_path *org_path = NULL;
+	struct ext4_ext_path *dest_path = NULL;
+	struct ext4_extent   *oext, *dext;
+	struct ext4_extent   tmp_ext;
+	int	err = 0;
+	int	depth;
+	ext4_fsblk_t from, count, dest_off, diff, replaced_count = 0;
+	handle_t *handle = NULL;
+	unsigned jnum;
+
+	from = (ext4_fsblk_t)from_page << 
+			(PAGE_CACHE_SHIFT - dest_inode->i_blkbits);
+	count = (ext4_fsblk_t)count_page <<
+			(PAGE_CACHE_SHIFT - dest_inode->i_blkbits);
+	dest_off = (ext4_fsblk_t)dest_from_page <<
+			(PAGE_CACHE_SHIFT - dest_inode->i_blkbits);
+	jnum = ext4_ext_writepage_trans_blocks(org_inode, count) + 3;
+	handle = ext4_journal_start(org_inode, jnum);
+	if (IS_ERR(handle)) {
+		err = PTR_ERR(handle);
+		goto out;
+	}
+
+	/* Get the original extent for the block "from" */
+	org_path = ext4_ext_find_extent(org_inode, from, NULL);
+	if (IS_ERR(org_path)) {
+		err = PTR_ERR(org_path);
+		org_path = NULL;
+		goto out;
+	}
+
+	/* Get the destination extent for the head */
+	dest_path = ext4_ext_find_extent(dest_inode, dest_off, NULL);
+	if (IS_ERR(dest_path)) {
+		err = PTR_ERR(dest_path);
+		dest_path = NULL;
+		goto out;
+	}
+	depth = ext_depth(dest_inode);
+	dext = dest_path[depth].p_ext;
+	/* When dext is too large, pick up the target range. */
+	diff = dest_off - le32_to_cpu(dext->ee_block);
+	ext4_ext_store_pblock(&tmp_ext, ext_pblock(dext) + diff);
+	tmp_ext.ee_block = cpu_to_le32(le32_to_cpu(dext->ee_block) + diff);
+	tmp_ext.ee_len = cpu_to_le16(le16_to_cpu(dext->ee_len) - diff);
+	if (count < tmp_ext.ee_len) {
+		tmp_ext.ee_len = cpu_to_le16(count);
+	}
+	dext = &tmp_ext;
+
+	/* loop for the destination extents */
+	while (1) {
+		/* The extent for destination must be found. */
+		BUG_ON(!dext || dest_off != le32_to_cpu(dext->ee_block));
+
+		/* loop for the original extent blocks */
+		if ((err = ext4_ext_defrag_leaf_block(handle, org_inode,
+			org_path, dext, &from, delete_start)) < 0) {
+			goto out;
+		}
+
+		replaced_count += le16_to_cpu(dext->ee_len);
+		dest_off += le16_to_cpu(dext->ee_len);
+		from += le16_to_cpu(dext->ee_len);
+
+		/* Already moved the expected blocks */
+		if (replaced_count >= count)
+			break;
+
+		/* get the next extent on both original and destination. */
+		err = ext4_ext_next_extent(dest_inode, dest_path, &dext);
+		if (err != 0) {
+			if (err > 0) {
+				err = 0;
+			}
+			goto out;
+		}
+		if ((err =
+			ext4_ext_next_extent(org_inode, org_path, &oext)) < 0) {
+			goto out;
+		}
+	}
+out:
+	if (handle) {
+		ext4_journal_stop(handle);
+	}
+	if (org_path) {
+		ext4_ext_drop_refs(org_path);
+		kfree(org_path);
+	}
+	if (dest_path) {
+		ext4_ext_drop_refs(dest_path);
+		kfree(dest_path);
+	}
+
+	return err;
+}
+
+/**
+ * ext4_ext_remove_index_blocks - remove leaf blocks and index blocks
+ * @handle      handle
+ * @dest_inode  temporary inode
+ * @eh          extent header
+ * @depth       depth of extent tree
+ *
+ * This function returns 0 if succeed, otherwise returns error value
+ */
+static int ext4_ext_remove_index_blocks(handle_t *handle,
+			struct inode *dest_inode,
+			struct ext4_extent_header *eh, int depth)
+{
+	struct ext4_extent_idx *idx;
+	struct buffer_head *bh;
+	int metadata = 1;
+	int credits = 0;
+	int i, ret = 0;
+
+	if (depth == 0) {
+		eh->eh_entries = 0;
+		return 0;
+	}
+
+	idx = EXT_FIRST_INDEX(eh);
+
+	for (i = 1; i <= eh->eh_entries; i++) {
+		if (depth > 1) {
+			bh = sb_bread(dest_inode->i_sb, idx->ei_leaf);
+			if (!bh) {
+				ret = -EIO;
+			} else {
+				ret = ext4_ext_remove_index_blocks(handle,
+					dest_inode, ext_block_hdr(bh),
+					depth - 1);
+				brelse(bh);
+			}
+		}
+#ifdef CONFIG_QUOTA
+		credits = 2 * EXT4_QUOTA_TRANS_BLOCKS(dest_inode->i_sb);
+#endif
+		handle = ext4_ext_journal_restart(handle,
+				credits + EXT4_TRANS_META_BLOCKS);
+		if (IS_ERR(handle))
+			return PTR_ERR(handle);
+
+		ext4_free_blocks(handle, dest_inode,
+				idx->ei_leaf, 1, metadata);
+		eh->eh_entries--;
+		idx++;
+	}
+	return ret;
+}
+
+/**
  * ext4_ext_alloc_blocks - allocate contiguous blocks to temporary inode
  * @dest_inode   temporary inode for multiple block allocation
  * @iblock       file related offset
@@ -2667,6 +3314,60 @@ out2:
 }
 
 /**
+ * ext4_ext_defrag_partial - defrag original file partially
+ * @filp:		pointer to file
+ * @org_offset:		page index on original file
+ * @dest_offset:	page index on temporary file
+ *
+ * This function returns 0 if succeeded, otherwise returns error value
+ */
+static int
+ext4_ext_defrag_partial(struct inode *tmp_inode,
+			struct file *filp,
+			pgoff_t org_offset,
+			pgoff_t dest_offset, ext4_fsblk_t *delete_start)
+{
+	struct inode *inode = filp->f_dentry->d_inode;
+	struct address_space *mapping = inode->i_mapping;
+	struct page *page;
+	pgoff_t offset_in_page = PAGE_SIZE;
+	int ret = 0;
+
+	page = read_cache_page(inode->i_mapping,
+		       org_offset, (filler_t *)inode->i_mapping->a_ops->readpage,
+		       NULL);
+
+	if (IS_ERR(page)) {
+		ret = PTR_ERR(page);
+		return ret;
+	}
+
+	lock_page(page);
+	/* release old bh and drop refs */
+	try_to_release_page(page, 0);
+	ret = ext4_ext_replace_branches(inode, tmp_inode, org_offset, 
+			dest_offset, 1, delete_start);
+	if (ret < 0)
+		goto ERR;
+
+	if (org_offset == ((inode->i_size - 1) >> PAGE_SHIFT))
+		offset_in_page = (inode->i_size & (PAGE_CACHE_SIZE - 1));
+
+	ret = mapping->a_ops->prepare_write(filp, page,
+					    0, offset_in_page);
+	if (ret)
+		goto ERR;
+
+	ret = mapping->a_ops->commit_write(filp, page,
+					   0, offset_in_page);
+ERR:
+	unlock_page(page);
+	page_cache_release(page);
+
+	return (ret < 0 ? ret : 0);
+}
+
+/**
  * ext4_ext_new_extent_tree -  allocate contiguous blocks
  * @inode:		inode of the original file
  * @tmp_inode:		inode of the temporary file

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